Craftr doesn't use the project tool but does invoke the R20 source preprocessor. I still use it over the project tool as it integrates in my existing ecosystem and I can compile for R19 and R20 without needing to keep multiple project files in sync.

Anyway, I won't be able to maintain Craftr intensively in the future, so if you create a plugin for R20+ only, I'd recommend using the project tool. ;-)